Recording your drum parts to a pre-recorded track is a very liberating experience. You don't have to bother about keeping the guys in time, remembering the structure or anything. Just play. If it works, keep it. If it doesn't work, bin it and try again.

This is a much harder attitude to assume if you have a restless band getting pissed off at you every time you fluff a take.

This was/is Copeland's studio strongpoint. This studio confidence also transfers nicely to his live work. If you know you can make it work in the studio then the strength of your character can force it through live. This may be why Sting disliked Stewart as a musician - inconsistant playing, great when he was great, sometimes not so great.